1. Field of the Invention
The present invention relates to a general purpose commercial printing machine or system for continuously producing huge volumes of printed matter.
2. Description of the Background Art
In general purpose commercial printing for production of printed matter such as newspaper, magazines, books and advertisements, huge volumes of printed matter are produced continuously from the same plate. To keep the quality of printed matter in such mass and continuous printing, it is necessary to produce proper and stable supplies of consumable ink and water used in a printing machine. This is because an excess or short ink supply causes a color irregularity in printed matter and an excess or short water supply causes skipping and blurring in printed matter; that is, an excess or short supply results in poor printed matter.
In a printing process, ink and water supply control has conventionally been performed based on a skilled printing-machine operator""s experience and intuition. The operator called a xe2x80x9cchief operatorxe2x80x9d determines and controls ink and water supplies as appropriate based on the characteristics of printing elements (characters or illustrations) such as color, shape, size and location, various conditions such as the surrounding environment of each printing machine (e.g., temperature and humidity) and ink viscosity, and past case examples of printing.
For ink supply control, the following automatic supply control methods such as color patch measurement and image comparison have also been used formerly.
(1) Color Patch Measurement Method
FIG. 22 is a diagram showing an example of color patches for use in this method. In FIG. 22, printing paper PP1 shall move in a print direction D1 indicated by the arrow for printing. On a margin region MG11 belonging to an ink supply region IS11 of the printing paper PP1, color patches PC, PM, PY and PK corresponding respectively to cyan (C), magenta (M), yellow (Y) and black (K) are printed. The color patch PC for cyan consists of four color patches PC1 to PC4 of different densities. The same can be said of the color patches PM, PY and PK. Although not shown, in ink supply regions IS12 and IS13 adjacent to the ink supply region IS11, color patches PC, PM, PY and PK are also printed similarly on their respective margin regions MG12 and MG13.
In the color patch measurement method, the densities of the color patches PC, PM, PY and PK are measured and compared with originally intended densities (reference chromaticity) after printing, and then differences in density (relative chromaticity) are fed back for ink supply control.
(2) Image Comparison Method
FIGS. 23A and 23B are diagrams for explaining the image comparison method. FIG. 23A shows part of image data DP1 contained within an ink supply region IS20. The image data DP1 is generated by photographing printed matter on printing paper PP2 at low resolution or scanning it with a scanner. C1 to C9 represent pixels in the image data DP1. FIG. 23B shows image data DST0 corresponding to the data shown in FIG. 23A, in a reference image PST0 to be printed. Pixels C1S to C9S correspond respectively to the pixels C1 to C9 in FIG. 23A. In both FIGS. 23A and 23B, the density of each pixel is expressed as the spacing between slant lines, where a narrower spacing represents a higher density.
In the image comparison method, relative chromaticity of corresponding pixels is calculated and the sum total of relative chromaticity for each supply region is fed back for ink supply control.
However, the conventional ink and water supply control methods have the following problems (hereinafter the ink supply is referred to as xe2x80x9cI supplyxe2x80x9d and the water supply as xe2x80x9cW supplyxe2x80x9d and both are generically referred to as xe2x80x9cI/W supplyxe2x80x9d).
First, I/W supply control by the xe2x80x9cchief operatorxe2x80x9d is only possible for an operator who has accumulated enough experience to acquire technical skills; that is, it is impossible for an inexperienced operator. This entails high labor costs involving the cost of training. Besides, it cannot always be said that optimal I/W supply control can be achieved, because different operators may form different judgments or a judgment made by an operator may not always be the best.
Secondly, in the automatic supply control methods such as color patch measurement and image comparison, only the sum total of relative chromaticity for each pixel is obtained and no consideration is given to the contents of an image such as image data size, color, texture, and importance of the contents (e.g., in the case of a portrait, either a subject or a background). Also in the color patch measurement method, the relative chromaticity is judged from the color patches as representatives, and therefore, it may not be possible to fully address a local color irregularity, skipping and the like in printed matter.
The present invention is directed to an ink or water supply controller in a general purpose commercial printing machine for continuously producing huge volumes of printed matter.
According to the present invention, the controller comprises the following: (a) an object region setting element for setting a plurality of object regions in a reference image to be printed, the object regions being set based on reference image data representing the reference image; (b) a read element for reading an image of printed matter corresponding to the reference image to obtain print image data; (c) a comparison element for comparing the reference image data and the print image data for each of the object regions to obtain an image comparison result; and (d) a control variable calculation element for calculating control variables for ink and water in the printing machine, the control variables being calculated based on both a regional characteristic and the image comparison result obtained for each of the object regions.
According to a preferred embodiment of the present invention, objective ink and water supply control can be achieved based on a difference between reference image data for printing and image data obtained from actual printed matter, for each of the object regions.
According to an aspect of the present invention, the regional characteristic includes, as a visual image characteristic of each of the object regions, at least one of the following: (1) a color characteristic of each of the object regions; (2) a texture characteristic of each of the object regions; and (3) a regional attribute depending on the type of a print image included in each of the object regions.
This permits supply control reflecting a visual characteristic of each of the object regions.
According to another aspect of the present invention, the regional characteristic includes, as a geometrical characteristic of each of the object regions in the reference image, at least one of the following: (1) a region size of each of the object region; (2) a location of each of the object regions in the reference image; (3) relative positions of each of the object regions and an ink key region of the printing machine; and (4) relative positions of each of the object regions and its adjacent regions.
This permits supply control reflecting a geometrical characteristic of each of the object regions.
An object of the present invention is, therefore, to provide a printing machine control technique that can set ink and water supplies more properly according to the contents of an image to be printed.